The National Ground Water Assn. (NGWA) announced that ...
A look at three tried-and-true methods for water softening & treatment
One of the most pronounced shifts in the water treatment industry is the rapidly burgeoning need to improve water quality. The need for water treatment systems is growing quickly, and, unfortunately, North America is hardly immune to challenges.
I thought it might be helpful to develop a water treatment primer in two parts. This installment looks at current technology and its applications to traditional methods of water treatment and softening. The second installment, which will appear in Water Quality Products this fall, will examine new and emerging technologies.
Ion Exchange Water Softeners
There are many ways that water can pose ongoing issues within a home’s piping system, but in terms of overall cost, water hardness takes the prize. Water typically is considered hard when the amount of calcium and magnesium exceeds 3 grains per gal; 1 grain is equal to 17.1 ppm of calcium carbonate.
Although there are about as many types of water softeners as there are water treatment manufacturers, the method of ion exchange is basically the same. The units typically consist of three main components: a pressure vessel, where the ion exchange process takes place; a separate tank, where the brine solution needed for regeneration (typically salt or potassium chloride) is stored; and a control valve that directs the flow of water during service and the regeneration cycle. In recent years, control valve manufacturers have been making great strides in optimizing salt efficiency.
How it works. Inside the pressure vessel are many thousands of tiny (0.5- to 1.2-mm) electrically charged polystyrene beads. These beads attract positively charged ions called cations. The resin beads are supercharged with sodium or potassium, both of which are cations, from the brine solution. Hard water containing cations such as calcium and magnesium will enter the inlet side of the valve and be directed to the ion exchange resin bed. The resin favors the more attractive hardness minerals. Calcium and magnesium hardness replace the sodium or potassium.
The regeneration cycle. Based on the valve’s programming or time clock setting, and depending on the style of softener, once the hardness minerals have completely exhausted the resin bed during normal service, the valve will trigger a regeneration cycle, sending the collected impurities down the drain. First, the ion exchange media (where the softening process takes place) are super-charged with the brine solution through the control valve, and then the excess brine is washed down the drain during a rinse cycle.
To a homeowner with a newly installed water softener, the benefits of having softened water are immediately clear. It makes for a richer lather and therefore greater soap efficiency within the home.
Reverse Osmosis Systems
Developed more than 40 years ago for large seawater desalination plants and other industrial uses, reverse osmosis (RO) technology has since been scaled down for point-of-use (POU) residential purposes to improve small quantities of water intended for drinking and cooking.
As its name suggests, RO is the reverse of the naturally occurring process of osmosis, which is how water is transported into and out of living cells. By applying pressure on the incoming higher solids/salt content supply side, semipermeable thin-film RO membranes allow only pure water to pass through.
This process requires a rinse line to move the impurities away from the membrane. This water must be discharged to drain, or a pump may be installed to redirect it for another purpose—typically back into the water heater or into a rainwater collection system. These systems are known in the water treatment industry as “zero-waste RO systems.”
The efficiency of any RO system is dependent upon three variables:
The RO feedwater must be pretreated in order to prevent membrane damage and/or premature fouling. There typically are two stages for residential RO pretreatment: a polypropylene sediment filter and a carbon filter for chlorine, taste and odor reduction.
In residential areas that are not supplied by a central, chlorinated municipal water source, other forms of disinfection, such as ultraviolet (UV), may be necessary. A UV system physically treats water by radiating the cells of microorganisms such as Cryptosporidium, Bacillus and E. coli, to name but a few, causing a molecular rearrangement of their DNA that renders them unable to self-reproduce inside a home’s water supply.
UV disinfection targets potentially harmful bacteria and viruses; it has no effect on the pH, taste, smell or appearance of the water.
Three important things to remember when sizing and installing UV systems are:
For residential water treatment, nothing saves more time and aggravation than a water analysis. Knowing what is in the water is the first step toward knowing how to properly treat it.
Don’t over- (or under-) do it — using the water quality report as a basis for suitable treatment, determine the size/capacity of the system by taking into consideration the incoming line size, fixture count and the number of people living in the house. The operative question is: What is needed?